Disclosed is a method and a device for detecting states of a battery and a battery pack. The disclosure obtains a first state of charge and a second state of charge of the battery by use of a charge calculation method and a method based on battery model, respectively. The charge calculation method is more accurate when the charge-discharge current is large and the method based on battery model performs better in handling a small current, so that a chemistry state of charge obtained by performing a weighted calculation for the first state of charge and the second state of charge can represent the real state of charge of the battery more precisely. The disclosure settles the difficulty on parameter extraction of the conventional model method, eliminates the influence of the accumulated error of the charge calculation method, and combines the advantages of the method based on the battery model and the coulometer method.